Content that users create on a service, like uploads, comments, articles.
User generated content is a "key characteristic for [the] so-called Web 2.0" ( http://en.wikipedia.org/wiki/User-generated_content , General requirements, 2013-01-10). It refers to content created by the users, as opposed to content created ready to consume by the service provider.
Users often have incentives to create content and contribute to services. These can be divided into more directly rewarding (for example, get a voucher for writing reviews) or indirect (be part of a community and stay in touch with friends by posting).
Questions tagged user-generated-content deal with the user experience considerations regarding this type of content, content strategy and its practical implementations.
- What is Web 2.0: Design Patterns and Business Models for the Next Generation of Software, Tim O'Reilly, O'Reilly Media, 2007)
- Exploring consumer motivations for creating user-generated content, T Daugherty, MS Eastin, L Bright - Journal of Interactive Advertising, 2008